The present invention is directed to a steam reformer for producing purified hydrogen including purified hydrogen for fuel cells.
Purified hydrogen is an important commodity in semiconductor, metallurgical, and chemical processing. It is also highly useful as a source of fuel for fuel cells, which can produce electrical power from hydrogen. There are a variety of means for producing purified hydrogen. Hydrogen can be liberated from hydrogen-containing compounds such as alcohol by reforming with steam at elevated temperatures over a catalyst bed. Since this reaction is endothermic, the heat can be supplied from an external burner, or the heat can be supplied in-situ by mixing some oxygen and partially burning some of the fuel. The former process is generally called steam reforming; when air or oxygen is mixed with the fuel to supply heat the process is referred to as autothermal or partial oxidation reforming. Once the reforming process has been completed, substantial percentages of carbon monoxide will exist in the reformed gas; this carbon monoxide may be further reacted in a water-gas shift catalyst bed to form hydrogen and carbon dioxide. This lowers the percentage of carbon monoxide in the reformed gas.
To create high purity hydrogen from the reformed gas mixture, means can be employed to separate the hydrogen, e.g. via a selective membrane. The high purity hydrogen can then be used in an industrial process, in a fuel cell for power generation or other applications requiring purified hydrogen. In some cases, hydrogen purification is not used; the reformed gas is sent to a fuel cell after a selective oxidation step to further reduce carbon monoxide levels. In the latter case, the reformer will generally require dewpoint control, careful attention to prevent high carbon monoxide levels, and integration means with the fuel cell to receive the spent gas after much of the hydrogen has been exhausted.
The technology for hydrogen purification is well known, such as disclosed in U.S. Pat. No. 5,861,137 entitled Steam Reformer With Internal Hydrogen Purification issued Jan. 19, 1999. The above patent discloses a hydrogen purification system and discusses the prior art and the state of the prior art. The need for a practical reformer, requiring a cost effective design is clear. The patent discloses a method and system for partially extracting of a portion of purified hydrogen from an appropriate fuel feedstock of hydrogen containing fuel and using the discharged raffinate, with a significant amount of hydrogen therein, as the fuel for operating the burner.
In addition to a significant number of patents, a substantial volume of other publications are available describing various systems and aspects of hydrogen purification including systems based on steam reforming. Nevertheless, there is continuing demand for an improved hydrogen purification system which is cost effective both initially and during its operating life, as well as readily adapted for efficient and cost effective servicing. There is a particular demand for a reformer with a low pressure drop in the burner air system.